Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC
Laboratory calibrations of the Cloud Droplet Probe (CDP) sample area and droplet sizing are performed using water droplets of known size, generated at a known rate. Although calibrations with PSL and glass beads were consistent with theoretical instrument response, liquid water droplet calibrations...
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ftdoajarticles:oai:doaj.org/article:b771fb8598ad40b4889bacfd8b550347 2023-05-15T15:17:33+02:00 Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC S. Lance C. A. Brock D. Rogers J. A. Gordon 2010-12-01T00:00:00Z https://doi.org/10.5194/amt-3-1683-2010 https://doaj.org/article/b771fb8598ad40b4889bacfd8b550347 EN eng Copernicus Publications http://www.atmos-meas-tech.net/3/1683/2010/amt-3-1683-2010.pdf https://doaj.org/toc/1867-1381 https://doaj.org/toc/1867-8548 doi:10.5194/amt-3-1683-2010 1867-1381 1867-8548 https://doaj.org/article/b771fb8598ad40b4889bacfd8b550347 Atmospheric Measurement Techniques, Vol 3, Iss 6, Pp 1683-1706 (2010) Environmental engineering TA170-171 Earthwork. Foundations TA715-787 article 2010 ftdoajarticles https://doi.org/10.5194/amt-3-1683-2010 2023-01-08T01:33:05Z Laboratory calibrations of the Cloud Droplet Probe (CDP) sample area and droplet sizing are performed using water droplets of known size, generated at a known rate. Although calibrations with PSL and glass beads were consistent with theoretical instrument response, liquid water droplet calibrations were not, and necessitated a 2 μm shift in the manufacturer's calibration. We show that much of this response shift may be attributable to a misalignment of the optics relative to the axis of the laser beam. Comparison with an independent measure of liquid water content (LWC) during in-flight operation suggests much greater biases in the droplet size and/or droplet concentration measured by the CDP than would be expected based on the laboratory calibrations. Since the bias in CDP-LWC is strongly concentration dependent, we hypothesize that this discrepancy is a result of coincidence, when two or more droplets pass through the CDP laser beam within a very short time. The coincidence error, most frequently resulting from the passage of one droplet outside and one inside the instrument sample area at the same time, is evaluated in terms of an "extended sample area" (SA E ), the area in which individual droplets can affect the sizing detector without necessarily registering on the qualifier. SA E is calibrated with standardized water droplets, and used in a Monte-Carlo simulation to estimate the effect of coincidence on the measured droplet size distributions. The simulations show that extended coincidence errors are important for the CDP at droplet concentrations even as low as 200 cm −3 , and these errors are necessary to explain the trend between calculated and measured LWC observed in liquid and mixed-phase clouds during the Aerosol, Radiation and Cloud Processes Affecting Arctic Climate (ARCPAC) study. We estimate from the simulations that 60% oversizing error and 50% undercounting error can occur at droplet concentrations exceeding 400 cm −3 . Modification of the optical design of the CDP is currently being explored ... Article in Journal/Newspaper Arctic Directory of Open Access Journals: DOAJ Articles Arctic Atmospheric Measurement Techniques 3 6 1683 1706 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Environmental engineering TA170-171 Earthwork. Foundations TA715-787 |
spellingShingle |
Environmental engineering TA170-171 Earthwork. Foundations TA715-787 S. Lance C. A. Brock D. Rogers J. A. Gordon Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC |
topic_facet |
Environmental engineering TA170-171 Earthwork. Foundations TA715-787 |
description |
Laboratory calibrations of the Cloud Droplet Probe (CDP) sample area and droplet sizing are performed using water droplets of known size, generated at a known rate. Although calibrations with PSL and glass beads were consistent with theoretical instrument response, liquid water droplet calibrations were not, and necessitated a 2 μm shift in the manufacturer's calibration. We show that much of this response shift may be attributable to a misalignment of the optics relative to the axis of the laser beam. Comparison with an independent measure of liquid water content (LWC) during in-flight operation suggests much greater biases in the droplet size and/or droplet concentration measured by the CDP than would be expected based on the laboratory calibrations. Since the bias in CDP-LWC is strongly concentration dependent, we hypothesize that this discrepancy is a result of coincidence, when two or more droplets pass through the CDP laser beam within a very short time. The coincidence error, most frequently resulting from the passage of one droplet outside and one inside the instrument sample area at the same time, is evaluated in terms of an "extended sample area" (SA E ), the area in which individual droplets can affect the sizing detector without necessarily registering on the qualifier. SA E is calibrated with standardized water droplets, and used in a Monte-Carlo simulation to estimate the effect of coincidence on the measured droplet size distributions. The simulations show that extended coincidence errors are important for the CDP at droplet concentrations even as low as 200 cm −3 , and these errors are necessary to explain the trend between calculated and measured LWC observed in liquid and mixed-phase clouds during the Aerosol, Radiation and Cloud Processes Affecting Arctic Climate (ARCPAC) study. We estimate from the simulations that 60% oversizing error and 50% undercounting error can occur at droplet concentrations exceeding 400 cm −3 . Modification of the optical design of the CDP is currently being explored ... |
format |
Article in Journal/Newspaper |
author |
S. Lance C. A. Brock D. Rogers J. A. Gordon |
author_facet |
S. Lance C. A. Brock D. Rogers J. A. Gordon |
author_sort |
S. Lance |
title |
Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC |
title_short |
Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC |
title_full |
Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC |
title_fullStr |
Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC |
title_full_unstemmed |
Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC |
title_sort |
water droplet calibration of the cloud droplet probe (cdp) and in-flight performance in liquid, ice and mixed-phase clouds during arcpac |
publisher |
Copernicus Publications |
publishDate |
2010 |
url |
https://doi.org/10.5194/amt-3-1683-2010 https://doaj.org/article/b771fb8598ad40b4889bacfd8b550347 |
geographic |
Arctic |
geographic_facet |
Arctic |
genre |
Arctic |
genre_facet |
Arctic |
op_source |
Atmospheric Measurement Techniques, Vol 3, Iss 6, Pp 1683-1706 (2010) |
op_relation |
http://www.atmos-meas-tech.net/3/1683/2010/amt-3-1683-2010.pdf https://doaj.org/toc/1867-1381 https://doaj.org/toc/1867-8548 doi:10.5194/amt-3-1683-2010 1867-1381 1867-8548 https://doaj.org/article/b771fb8598ad40b4889bacfd8b550347 |
op_doi |
https://doi.org/10.5194/amt-3-1683-2010 |
container_title |
Atmospheric Measurement Techniques |
container_volume |
3 |
container_issue |
6 |
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1683 |
op_container_end_page |
1706 |
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